ACTIVITY and sign : grounding mathematicas education / Michael H.G. Hoffmann, Johannes Lenhard, Falk Seeger (Editors). - New York [etc.] : Springer Science+Business Media, 2005. - 389 str. : ilustr. ; 25 cmBibliografije uz radove. - Kazalo.ISBN 0-387-24269-4. - 0-387-24270-8